class_docstr: Represents an interval containing floating points as start and
  end of the interval
  The is_valid variable tracks whether the interval obtained as the
  result of the function is in the domain and is continuous.
  - True: Represents the interval result of a function is continuous and
          in the domain of the function.
  - False: The interval argument of the function was not in the domain of
           the function, hence the is_valid of the result interval is False
  - None: The function was not continuous over the interval or
          the function's argument interval is partly in the domain of the
          function
  
  A comparison between an interval and a real number, or a
  comparison between two intervals may return ``intervalMembership``
  of two 3-valued logic values.
code: def __str__(self):
      return "[%f, %f]" % (self.start, self.end)
  
imports: from sympy.core.numbers import int_valued
  from sympy.core.logic import fuzzy_and
  from sympy.simplify.simplify import nsimplify
  from .interval_membership import intervalMembership
label_desc: Use image node_id 5 for calling the interval obj's underlying member method code with example usage: obj.__str__() and returns: unknown